Linkage between moisture transport over the Yangtze River Basin and a critical area of the Tibetan Plateau during the Meiyu

Located downstream of the Tibetan Plateau (TP), the Yangtze River Basin (YRB) in China frequently experiences torrential rainfall and severe rainstorms within the zonally elongate Meiyu belt. Inter-annual variations in drought and flooding in the YRB are shown to be highly correlated with the upstream surface latent heat flux (SLHF) over the TP, suggesting that the SLHF over the TP can be a “strong signal” of Meiyu variability. Results show that the southeastern margin of the TP (SEMTP) is the most “sensitivity area” of the “strong signal”. On inter-annual scales, low (high) SLHF over the SEMTP corresponds to high (low) humidity at upper levels, strong (weak) zonal moisture transport and a southerly (northerly) pattern of East Asian summer monsoon (EASM) moisture transport circulation in July. The anomalous moisture flow originating from the mid to low latitude oceans, converges in the east of the SEMTP and turns eastward (northward); thus, the SEMTP acts as the key area of redirection of moisture flow. The ridge of moisture transport is located at about 22.5°N (29.5°N) in East China for low (high) SLHF over the SEMTP. Under low SLHF conditions, the warm, humid airflow from the SEMTP creates favorable conditions for Meiyu rainfall and torrential rainstorms. Numerical simulation and sensitivity analyses using the mesoscale Weather Research and Forecasting (WRF) model further reveal that SLHF over the SEMTP shows pronounced “strong signal” features. The variation of intensity of SLHF over the SEMTP corresponds to the moisture transport structure of the Meiyu rain belt and the location of the ridge of the subtropical high in East China. An increase in the apparent heat source Q1 over the main body of the TP might explain the “strong signal” over the SEMTP. This apparent heat source plays an important role in modulating both the SLHF over the SEMTP and the location of the subtropical high circulation system.